This invention relates generally to electric motors and more particularly, to a motor enclosure that incorporates a mid shield for electric and electronically commutated motors.
Known electronically commutated motors have a multi-stage winding assembly and a magnetic assembly associated for relative rotation. The winding stages of the multi-stage winding assembly have a preset energization sequence that includes at least one unenergized winding stage in which an induced back EMF appears. When integrated over time to a predetermined value, the induced back EMF indicates the instant at which the relative angular position between the multi-stage winding assembly and the magnetic assembly is suitable for the sequential commutation of the next winding stage.
The electronic circuitry for an electronically commutated motor generally includes a power circuit, a regulating circuit, and a control circuit. The power circuit has solid state switching devices for commutating the power supplied to the electronically commutated motor to effect its energization. The regulating circuit includes various solid state components for maintaining the power supplied to the electronically commutated motor generally constant. The control circuit, sometimes referred to as a control unit, has various solid state components for controlling the conductivity of the switching devices.
Some of the solid state components for an electronically commutated motor, e.g., transistors, need to be relatively large to accommodate the currents that must pass through them. Large transistors can produce a sizable amount of heat that should be dissipated in order to keep the transistors functioning properly. It is well known in the art that to promote heat dissipation, the electronic circuitry for an electronically commutated motor can be attached to a heat sink and positioned adjacent an outer surface of an end shield of the motor. However, this increases costs since another compartment is needed to protect the electronic circuitry. Also complexity is increased when servicing such motors because removal of the end shield generally means that the windings and rotating shaft of such motors are free to move about the motor enclosure.